Method of manufacturing an optical fibre suitable for high transmission rates

ABSTRACT

The present invention relates to a method of manufacturing an optical fibre suitable for high transmission rates, which method comprises: i) supplying one or more glass forming precursors, and possibly a dopant, to a quartz substrate tube, ii) forming a plasma in the quartz substrate tube for the purpose of bringing about a reaction mixture so as to form glass layers, which may or may not be doped, on the interior of the substrate tube, iii) collapsing the substrate tube obtained in step ii) into a perform while heating, and iv) drawing an optical fibre from the perform while heating. The present invention furthermore relates to an optical fibre suitable for high transmission rates.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. patent application Ser. No.10/093,088, filed Mar. 6, 2002, now pending, which application isincorporated herein by reference in its entirety.

TECHNICAL FIELD

The present invention relates to a method of manufacturing an opticalfibre suitable for high transmission rates, which method comprises thesteps of:

-   -   i) supplying one or more glass forming precursors, and possibly        a dopant, to a quartz substrate tube,    -   ii) forming a plasma in the quartz substrate tube for the        purpose of bringing about a reaction in the reactive mixture so        as to form glass layers, which may or may not be doped, on the        interior of the substrate tube,    -   iii) collapsing the substrate tube obtained in step ii) into a        preform while heating,    -   iv) drawing an optical fibre from the preform while heating.

The present invention furthermore relates to an optical fibre suitablefor high transmission rates.

BACKGROUND INFORMATION

Such a method is known per se from U.S. Pat. Nos. 4,793,843 and5,188,648 granted to the present applicant. From said the documents itis known that part of the dopant in the layers in the center mayevaporate upon collapsing of the quartz substrate tube while heating.Said evaporation results in a disturbance of the refractive indexprofile in the final fibre. Said disturbance of the refractive indexprofile has an adverse effect on the bandwidth of the optical fibre.

The future developments in the telecommunication industry include thetransmission of information at ever higher bit rates (bits/sec) overeven longer distances. The present data networks use relatively low bitrates. Thus, light emitting diodes (LED) have so far been the mostcommon light source in these applications. Because of the demand fordata transmission rates which are higher than the modulation capacity ofLEDs, laser sources will be used instead of LEDs. This shift manifestsitself in the use of systems which are capable of supplying informationat rates as defined in the GigabitEthernet Standard (IEEE 802.3z. 1998)and higher rates. GigabitEthernet Standard corresponds to a transmissionrate of 1.25 Gigabit/sec.

The multimode optical fibre that is currently used in telecommunicationsystems has mainly been designed for being used with such LED lightsources. In addition, said multimode fibre has not been optimized foruse with the laser sources that are present in systems that have beendesigned for transmitting information at rates equal to or higher thanGigabitEthernet. In other words, laser sources impose different demandson the quality and the design of a multimode fibre than LED sources.Especially, the refractive index profile in the center of the core ofmultimode fibres is of major importance, in which in particular aprecisely defined parabolic profile is required so as to prevent adecrease of the information transmission rates. Accordingly, minordeviations in the center of the fibre profile may cause significantdisturbances in the output signal, which disturbances have a majorinfluence on the behavior of the system. This effect may manifest itselfin the form of a very small bandwidth or a very high jitter, or both.

The wavelengths at which the data transmission in such fibres takesplace are, respectively, the 850 m band, which is defined as 770 nm-920nm herein, and the 1300 nm band, which is defined as 1260 nm-1360 nmherein.

BRIEF SUMMARY OF THE INVENTION

The object of the present invention is thus to provide a method ofmanufacturing an optical fibre suitable for being used in a multimodetransmission system which is capable of transmitting data at rates equalto or higher than 1 Gigabit/sec. Such a multimode transmission systemcomprises a laser source, which transmits information at a rate of atleast 1.25 Gigabit/sec, and a multimode optical fibre, which isirradiated by the laser source.

The object of the present invention is furthermore to provide amultimode optical fibre suitable for transmitting information withGigabitEthernet in the 1300 nm band over a distance of at least 1000 m.

The object of the present invention is furthermore to provide amultimode optical fibre suitable for transmitting information withGigabitEthernet in the 1300 nm band over a distance of at least 550 m aswell as for transmitting information with GigabitEthernet in the 850 nmband over a distance of at least 550 m.

The object of the present invention is furthermore to provide amultimode optical fibre suitable for transmitting information at a rateof at least 10 Gigabit/sec in the 850 nm band over a distance of atleast 300 m.

The object of the present invention is furthermore to provide amultimode optical fibre suitable for transmitting information at a rateof at least 10 Gigabit/sec in the 850 nm band over a distance of atleast 300 m, in which said fibres have an OFL bandwidth of more than 500Mhz.km.

Another object of the present invention is to provide a method ofmanufacturing optical fibres, which optical fibres are fully compatiblefor use with high-rate laser sources as well as with LED sources.

DETAILED DESCRIPTION

According to the present invention, the present method as referred to inthe introduction above is characterized in that the glass layers, whichmay or may not be doped, are deposited on the interior of the substratetube in such a manner that separate layers are obtained after steps iii)and iv) in a region having a diameter of 10 μm at the most in the centerof the optical fibre that is finally drawn, wherein at least one of saidseparate layers has a surface area of 2 μm² at the most, wherein therefractive index value in the fibre that is finally drawn increases inthe direction of the center thereof.

Using such a method, a very well-defined, layered structure of the coreof the optical fibre is possible, as a result of which a preciselydefined refractive index profile is obtained in the final fibre, inwhich the light pulse that is passed through the fibre will only widento a minor extent, as a result of which the fibre will have a hightransmission capacity.

It is in particular preferred for the layers that have been separatelyobtained in a region having a diameter of 10 μm at the most in thecenter of the optical fibre to have mutually different refractive indexvalues.

The refractive index value of each layer can be influenced by supplyinga dopant to the reactive mixture of glass forming precursors which has ahigher refractive index value than said glass forming precursors. Saidinfluencing can take place, for example, by varying the composition ofthe gaseous mixture that is to be supplied to the quartz substrate tube.The layer thickness can be influenced by varying the gas speed, thespeed at which the plasma moves past the substrate tube and the plasmacapacity itself.

It is in particular preferred to deposit the glass layers, which may ormay not be doped, on the interior of the substrate tube in such a mannerthat separate layers are obtained in a region having a diameter of 10 μmat the most in the center of the fibre that is finally drawn, whereineach individual layer has a surface area of 1 μm² at the most, whereinthe refractive index value in the fibre that is finally drawn increasesin the direction of the center thereof.

The present invention furthermore relates to an optical fibre which ischaracterized in that said optical fibre is suitable for datatransmission rates of at least 1 Gigabit/sec over a distance of at least1000 m at a wavelength in the range of 1300 nm, wherein separate layersare obtained in a region having a diameter of 10 μm at the most in thecenter thereof, wherein at least one of said separate layers has asurface area of 2 μm² at the most, in particular 1 μm² at the most,wherein the refractive index value in the fibre that is finally drawnincreases in the direction of the center thereof.

The present invention furthermore relates to a multi mode optical fibrewhich is characterized in that it is suitable for transmittinginformation at a rate of at least 1 Gigabit/sec in the 1300 nm band overa distance of at least 550 m and which is suitable for transmittinginformation at a rate of at least 1 Gigabit/sec in the 850 nm band overa distance of at least 550 m, wherein separate layers are obtained in aregion having a diameter of 10 μm at the most in the center of the fibrethat is finally drawn, wherein at least one of said separate layers hasa surface area of 2 μm² at the most, in particular 1 μm² at the most,wherein the refractive index value in the fibre that is finally drawnincreases in the direction of the center thereof.

The present invention furthermore provides a multimode optical fibresuitable for transmitting information at a rate of at least 10Gigabit/sec in the 850 nm band over a distance of at least 300 m,wherein separate layers are obtained in a region having a diameter of 10μm at the most in the center of the fibre that is finally drawn, whereinat least one of said separate layers has a surface area of 2 μm² at themost, in particular 1 μm² at the most, wherein the refractive indexvalue in the fibre that is finally drawn increases in the direction ofthe center thereof.

The present invention is furthermore characterized by a multimodeoptical fibre suitable for transmitting information at a rate of atleast 10 Gigabit/sec in the 850 nm band over a distance of at least 300m, wherein said fibres have an OFL (“Over Filled Launch”, measuredbandwidth upon irradiation with an LED) bandwidth of more than 500Mhz.km at 1300 nm, wherein separate layers are obtained in a regionhaving a diameter of 10 μm at the most in the center of the fibre thatis finally drawn, wherein at least one of said separate layers has asurface area of 2 μm² at the most, in particular 1 μm² at the most,wherein the refractive index value in the fibre that is finally drawnincreases in the direction of the center thereof.

The present invention will be explained in more detail hereinafter bymeans of a number of examples, in which it should be noted, however,that the conditions used in the examples are merely described by way ofillustration and should not be construed as being limitative. The term“cladding diameter” comprises the overall diameter of the optical fibre,excluding an external coating capable of being stripped which may bepresent.

EXAMPLES Comparative Example 1

A multimode optical fibre was produced by means of the PCVD technique asdescribed in steps i)-iv). During step i), 960 core layers havingpractically the same volume were deposited in the substrate tube, withthe refractive index of each layer being increased in comparison withthe preceding layer by changing the proportion of the glass formingprecursors SiCl₄ and GeCl₄ that were supplied to the substrate tube. Therefractive index profile was so controlled that the final fibre would besuitable for use on both the wavelength bands of 850 nm and 1300 nm thatare frequently used at present. The preform thus obtained aftercollapsing in accordance with step iii) was drawn into an optical fibrehaving a core diameter of 62.5 μm and a cladding diameter of 125 μm. Thelayers in the optical fibre thus obtained appeared to have a surfacearea of 3.2 μm² each.

The fibre was subjected to a transmission test, using an 850 nm laser ata transmission rate of 1.25 Gigabit/sec. The maximum transmissiondistance for this fibre was 350 m, which value is too low to meet thepresent requirements.

Example 1

An optical fibre was produced by carrying out the same steps as incomparative example 1, with this difference that 2750 core layers weredeposited so as to form a fibre having a core diameter of 62.5 μm. Thelayers in the optical fibre thus obtained each had a surface area of 1.1μm². A transmission test of this fibre yielded a maximum transmissiondistance of 600 m at 1.25 Gigabit/sec and an 850 nm laser.

Comparative Example 2

Optical fibres were produced by carrying out the steps of example 1,wherein the refractive index profile was so controlled, however, thatthe fibre is optimized for use in the 850 nm band. The fibre, whoseindividual layers each had a surface area of 3.2 μm², was subjected to atransmission test of 10 Gigabit/sec. The maximum transmission distanceat this bit rate through said fibre amounted to 250 m, which value doesnot meet the present requirement with regard to the transmissiondistance.

Example 2

An optical fibre produced by carrying out the steps of example 1, inwhich fibre the individual layers each had a surface area of 1.1 μm²,transmitted a signal at 10 Gigabit/sec over a maximum distance of 350 m.

Example 3

A number of multimode optical fibres having a core diameter of 50 μmwere produced by means of the PCVD technique as described in stepsi)-iv). During step i), ±1600 core layers having practically the samevolume were deposited in the substrate tube, with the refractive indexof each layer being increased in comparison with the preceding layer bychanging the proportion of the glass forming precursors SiCl₂ and GeCl₄that were supplied to the substrate tube. The various refractive indexprofiles were so controlled that an optimum performance was obtained inthe 850 nm band or in the 1300 nm band. The deposited layers in saidfibres each had a surface area of 1.2 μm² each.

The fibres were subjected to transmission tests in both transmissionbands at a transmission rate of 1.25 Gigabit/sec, the results of whichtests are summarized below. From the table it is apparent that all themeasured values meet the present requirements with regard to thetransmission distance. Lowest value of Average value of TransmissionNumber of max. transmission max. transmission band fibres distancedistance  850 nm 12  960 m 1010 m 1300 nm 15 2020 m 2140 m

Example 4

A multimode optical fibre was produced by means of the PCVD technique asdescribed in steps i)-iv). In step i), 550 core layers having arelatively large volume were first deposited in the substrate tube,followed by the deposition of 120 core layers having a smaller volume,with the refractive index of each layer being increased in comparisonwith the preceding layer by changing the proportion of the glass formingprecursors SiCl₄ and GeCl₄ that were supplied to the substrate tube. Therefractive index profile was so controlled that the final fibre would besuitable for use on the wavelength bands of 850 nm and 1300 nm. Thepreform thus obtained after collapsing in accordance with step iii) wasdrawn into an optical fibre having a core diameter of 62.5 μm and acladding diameter of 125 μm. The layers in the optical fibre thusobtained appeared to have a surface area of 1.1 μm² each in a regionhaving a diameter of 10 μm in the center of the fibre. A transmissiontest of this fibre, using an 850 nm laser, yielded a maximumtransmission distance of 600 m at a transmission rate of 1.25Gigabit/sec. From this it became apparent that in particular the layersin the central portion of the optical core of the fibre must have asmall surface area in order to meet the objective of the invention. Thelayers outside the central portion of the optical fibre having adiameter of 10 μm, on the other hand, may have a surface area of morethan 2 μm².

1. A method of manufacturing a multimode optical fibre suitable fortransmission rates equal to or higher than 1 Gigabit/sec, of the methodcomprising: i) supplying one or more glass forming precursors, andpossibly a dopant, to a quartz substrate tube; ii) forming a plasma inthe quartz substrate tube for the purpose of bringing about a reactionin a reactive mixture so as to form glass layers, which may or may notbe doped, on an interior of the substrate tube; iii) collapsing thesubstrate tube obtained in ii) into a perform while heating; and iv)drawing an optical fibre from the perform while heating, wherein: theglass layers, which may or may not be doped, are deposited on theinterior of the substrate tube in such a manner that separate layersaccording to ii) are formed in a region having a diameter of 10 μm atmost in a center of an optical fibre that is finally drawn, wherein atleast one of said separate layers has a surface area of 2 μm² at most,wherein a refractive index value in the fibre that is finally drawnincreases in a direction of the center thereof.
 2. A method according toclaim 1 wherein the glass layers, which may or may not be doped, aredeposited on the interior of the substrate tube in such a manner thatseparate layers according to ii) are formed in the region having thediameter of 10 μm at the most in the center of the optical fibre that isfinally drawn, wherein at least one of said separate layers has asurface area of 1 μm² at most, wherein the refractive index value in thefibre that is finally drawn increases in the direction of the centerthereof.
 3. The method of claim 1 wherein the separate layers in theregion having the diameter of 10 μm at the most have mutually differentrefractive index values.
 4. The method of claim 3, further comprisingsupplying the dopant to the reactive mixture, the dopant having a higherrefractive index value than the glass forming precursor, so as toinfluence the refractive index value in each layer.
 5. The method ofclaim 4 wherein influencing the reactive index value in each layerincludes varying a composition of a gaseous mixture that is supplied tothe quartz substrate tube.
 6. The method of claim 1, further comprisinginfluencing a thickness of one or more of the layers by varying a speedat which the plasma moves past the substrate tube or by varying plasmacapacity.
 7. The method of claim 1, further comprising changing aproportion of different glass forming precursors, which are supplied tothe quartz substrate tube, relative to each other so as to providedifferent refractive index values for adjacent layers.
 8. A method tomanufacture a multimode optical fibre suitable for transmission ratesequal to or higher than 1 Gigabit/sec, the method comprising: i)supplying one or more glass forming precursors, and possibly a dopant,to a quartz substrate tube; ii) forming a plasma in the quartz substratetube to bring about a reaction so as to form glass layers, which may ormay not be doped, on an interior of the substrate tube; iii) collapsingthe substrate tube obtained in ii) into a preform while heating, iv)drawing an optical fibre from the preform while heating, wherein: theglass layers, which may or may not be doped, are deposited on theinterior of the substrate tube in such a manner that separate layers areobtained after iii) and iv) in a region adjacent to a center of anoptical fibre that is finally drawn, wherein a refractive index value inthe fibre that is finally drawn increases in a direction of the centerthereof, wherein the separate layers in the region of the optical fibrehave mutually different refractive index values.
 9. The method of claim8, further comprising supplying the dopant, the dopant having a higherrefractive index value than the glass forming precursor, so as toinfluence the refractive index value in each layer.
 10. The method ofclaim 9 wherein influencing the reactive index value in each layerincludes varying a composition of a gaseous mixture that is supplied tothe quartz substrate tube.
 11. The method of claim 8, further comprisinginfluencing a thickness of one or more of the layers by varying a speedat which the plasma moves through the substrate tube.
 12. The method ofclaim 8, further comprising influencing a thickness of one or more ofthe layers by varying plasma capacity.
 13. The method of claim 8,further comprising changing a proportion of different glass formingprecursors, which are supplied to the quartz substrate tube, relative toeach other so as to provide different refractive index values for thelayers.